Aerodynamic Heating Rocks Due to Impacts 3.Sterilization During the Launch

Home , McMurdo (crater), Mojave (crater)

Assessment of microbial contamination probability for sample return from Martian moons

Kosuke Kurosawa1, Kazuhisa, Fujita2, Hidenori Genda3, Ryuki Hyodo3, Takashi Mikouchi4 & Phobos/Deimos Microbial Contamination Assessment Team2

1Chiba Institute of Technology, 2JAXA, 3Tokyo Institute of Technology, 4The University of Tokyo

2018 9/19 Brief summary SterLim data Impact physics •Impact test Orbital dynamics •Heat test Stochastic analyses •Radiation test

The spatial distribution The current microbe of microbes density on the moons

☆The total survived fraction of microbes at the present is only ~2 ppm on Phobos and ~50 ppm on Deimos.

☆Heterogeneous distribution of the microbes on the Martian moons

☆Microbe contamination probability of collected samples can be below 10-6 by appropriately choosing the sampling approaches. Each step considered in this study

5.Impact processes 7. The formation of radiation on the moon’s surface shield by natural meteoroids -Sterilization by shocks -Fragmentation -Mixing with the regolith 6. Sterilization -Dispersion by radiation 2.The launch of Mars 4.Sterilization by aerodynamic heating rocks due to impacts 3.Sterilization during the launch

1.Potential microbial living on Mars Each step considered in this study

1.Potential microbial living on Mars Difference from SterLim study SterLim view Our view Homogeneous deposition by averaging “Mars-rock bombardment” incoming flux to the uppermost layer & Impact physics

Microbe distribution -Patchy in the horizontal direction -Depth-dependent Significant/Moderate/Minor effects SterLim Our work 1.Potential microbes Assuming same microbial Similar to SterLim, living on Mars density as Atacama Desert but a downward revision is introduced.

Analytic model given by 3-D hydrodynamic simulations to obtain 2.The launch of Mars rocks the point-source theory appropriate initial conditions due to impacts (The same used by Melosh) for the trajectory analyses

Sterilization during the launch based on 3.Sterilization during Not considered the data compilation of Martian meteorites the launch and recent finding on shock heating

4.Sterilization by Thermal analysis of Mars ejecta Not considered aerodynamic heating conducted along trajectories

5-1. Impact sterilization Microbe survival rate ~ 0.1 A revised-impact sterilization model

on the moon’s surface regardless of impact velocity to treat vimp dependence

Crater formation by Mars ejecta with 5-2. Impact processes Homogeneous deposition by retention & scattering of Mars ejecta on the moon’s surface averaging the incoming flux fragments taken into account

Sterilization model Same as SterLim, but the effects 6. Sterilization by radiation constructed by experiments of the depth is also considered.

7. The formation of radiation Not considered A new stochastic model shield by natural meteoroids Outline 1. General assumptions

2. Transportation to the moons

3. Mars-rock bombardment on the moon

4. Background impact flux by natural meteoroids

5. The change in the microbe density with time

6. Microbe contamination risk assessment

7. Conclusions Outline 1. General assumptions

2. Transportation to the moons

3. Mars-rock bombardment on the moon

4. Background impact flux by natural meteoroids

5. The change in the microbe density with time

6. Microbe contamination risk assessment

7. Conclusions General assumptions - Potential microbe density on Mars - Supporting data (SterLim data) - Source crater Potential microbe density on Mars Terrestrial Mars analog Condition Location Microbe concentration

106 – 108 CFU/kg Yungay [Navarro-González+03; Maier+04] Hyperarid (Atacama Desert) 108 – 1010 cells equivalent/kg [Glavin+04; Drees+06; Lester+07; Connon+07]

6 7 Cold & Arid McMurdo Dry valley 10 – 10 cells equivalent/kg (Antarctic permafrost) [Goordial+16]

8 Initial microbe density nMars = 10 CFU/kg

※1 CFU/kg ~ 102 cells/kg Potential microbe density on Mars [Data are taken from Navarro-González+03]

Not detected McMurdo Dry valley (Antarctic permafrost) [Goordial+16]

※1 CFU/kg ~ 102 cells/kg was assumed. Potential microbe density on Mars Terrestrial Mars analog Condition Location Microbe concentration

106 – 108 CFU/kg Yungay [Navarro-González+03; Maier+04] Hyperarid (Atacama Desert) 108 – 1010 cells equivalent/kg [Glavin+04; Drees+06; Lester+07; Connon+07]

6 7 Cold & Arid McMurdo Dry valley 10 – 10 cells equivalent/kg (Antarctic permafrost) [Goordial+16]

8 Initial microbe density nMars = 10 CFU/kg

※1 CFU/kg ~ 102 cells/kg Supporting data on sterilization The best systematic dataset to consider the case of Martian moons. SterLim impact test SterLim radiation test

[Patel+18] [Patel+18]

A different empirical model Time constant of MS2 was used based on the dataset was used. for conservative estimate. (Next slide) Impact survival rate The SterLim study assumed the survival rate is ~0.1.

[Patel+18]

Physical constraint: Survival rate must be decrease with increasing vimp because post shock temperature ∝ v2 An empirical model ± × −6 1.8 NΤN0 = exp − 9.5 4.3 10 Vimp Main source crater

Zunil crater Diameter: 10.1 km Longitude: 166 deg. East Latitude: 7.7 deg. North (Near the equator)

Impact direction: East-NorthEast [Preblich+07]

Formation age: 0.1–1 Myr ago [Hartmann+10]

[Preblich+07] The youngest-ray crater on Mars with a diameter of >10 km The other craters Transported mass to Phobos vs Formation age

Transported mass Mtransported Age estimate Mojave (58 km) Hartmann+10 was estimated in this study. Hartmann+10 (discuss later) using Malin+06 data [Hyodo+, to be submitted] Golombek+14 Werner+14 Tooting (29 km) Mtransported strongly depends on Df. -> The smaller craters are McMurdo (23 km) not important.

Zunil (10 km) Corinto (14 km) The other large craters are much older than Zunil.

-> The microbes must be sterilized at the present. (Next slide) Required time treq for radiation sterilization N0 treq = TC(H)ln Nth For conservative estimate,

Zunil 7 N0 = 10 (CFU/kg) -5 Nth = 10 (CFU/kg)

(Req-10 for 100 g sampling) The others The

Target depth Depth (cm) treq(years) for sampling <0.04 2.0 x 103 1 4.4 x 105 10 1.7 x 106 30 2.0 x 106 The microbes from the other craters must be sterilized until now. Outline 1. General assumptions

2. Transportation to the moons

3. Mars-rock bombardment on the moon

4. Background impact flux by natural meteoroids

5. The change in the microbe density with time

6. Microbe contamination risk assessment

7. Conclusions Launch Difficulties in the estimation of the mass of high-speed ejecta

High-speed ejection at velocities higher than ~20% of vimp cannot be treated by the widely-used point-source theory [Melosh84; Kurosawa&Takada19]

<-Velocity-volume behavior in the point-source theory

※The previous studies used the point-source theory ? [Chappaz+13; SterLim study]

[Housen & Holsapple11] Numerical simulations are necessary

to address the total mass of high-speed ejecta Mej. 3-D SPH simulation A three-dimensional Smoothed Particle Hydrodynamics code was used. [Genda+15; Kurosawa+18; Genda+, in prep.]

12 km/s, 45 degrees )

p 3

Particlevelocity(km/s) R 2 1 0 -1 -2

Height from the surface ( the surface from Height -3 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5

Horizontal distance from the impact point (Rp) [Genda+, in prep.] Calculation conditions •Granite projectile onto Granite target (Tillotson EOS) •Impact velocity v : 6, 9, 12, 15, 18 km/s imp Total 30 runs •Impact angle qimp: 15, 30, 45, 60, 75, 90 degrees •No gravity and strength (Scale-free calculation) Experimental validation [Okamoto, Kurosawa, Genda & Matsui, to be submitted] Laboratory experiment 3-D SPH simulation

(a) 0.0 ms (0.0) 5 mm (d) 0.0 ms (0.0) 5 mm 3.56 km/s Projectile 45 degrees (Polycarbonate) Projectile Target surface Impact Impact (Polycarbonate) direction Target surface direction

(b) 1.2 ms (0.89) (e) 1.2 ms (0.89)

Strongly depends on

both vimp and qimp Consistent with Artemieva&Ivanov04 Zunil-forming impact conditions Given that we know the projectile size,

the absolute value of Mej can be obtained. -> We searched for the impact conditions that reproduce

the observed crater diameter Df of the Zunil crater (10.1 km) Crater scaling laws [Schmidt & Housen87] β 1 1 − CD = 1.4 π 4π ρp 3 1−β 2β D = 3 C 3 D g−β v sinθ β = 0.17 tr D ρ p imp imp 6 3 t (Dry sand) An empirical law for crater collapse [McKinnon+91] −0.13 1.13 D = 7 km for Mars [Pike88] Df = 1.2Dc Dtr c

Impact velocity distribution: Rayleigh [Zahnle+03] Averaged impact velocity onto Mars = 14 km/s [Ito&Malhotra06]

Impact angle distribution: sin(2qimp) [Shoemaker62] Zunil-forming impact conditions

Averaged projectile diameter & mass 61 (1.8 km, 1013 kg)

38 kg)

22 12

4.8

1.4

1s bound Projectile mass (10 Projectile q 0.18 due to vimp& imp distributions (10,000 Monte Carlo runs) Sterilization during ejection Sterilization during the launch Major (>1 kg) Martian meteorites having young ejection ages (~1 Myr)

Name Ejection age (Myr) Mass (kg) Ppeak (GPa) Tpost_calc – T0(K) EETA79001 0.73±0.15 7.94 34±2 250±50 Same event Tissint 0.7±0.3 7-11 [e.g., Chennaoui DaG 476 1.24±0.12 2.02 35–40 400±50 Aoudjehane+12] SaU 005 1.5±0.3 1.34 35–40 400±50 [Nyquist+01; Chennaoui Aoudjehane+12] The estimated temperature are from thermodynamic calculations, NOT from any measurements.

ln(N/N0) ~ -2.5 -> N/N0 ~ 0.1 Martian meteorites possibly related to Zunil The survival rate immediately after the launch is likely to be ~0.1.

SterLim Heat test [Patel+18] Roles of Plastic deformation [Kurosawa & Genda18] The estimated-post-shock temperatures are likely to be underestimated.

2-D iSALE calculations Dunite->Dunite (ANEOS)

vimp = 3 km/s qimp = 90 degrees

The degree of shock heating is significantly higher than the case of purely hydrodynamic.

“This heat source has surprisingly escaped explicit attention for decades” [Comments by Melosh & Ivanov18, GRL] High-resolution numerical model 2-D iSALE shock physics code allows us to address the degree of shock heating during impact spallation. [Kurosawa+18] Basalt -> Basalt (ANEOS) vimp = 3.5 km/s (The normal component of 5 km/s at 45 degrees) 1000 cells per projectile radius Elasto-plastic Hydrodynamic [Parameters are taken from Ivanov+10] With black circles Particles moving at >3.8 km/s Incipient melting

Sterilization

Consistent with Artemieva & Ivanov04 High-resolution numerical Low-temperature ejection is hardmodelto be explained by impact physics. 2-D iSALE shock physics code allows us to address Unknown special condition(s) is required for ejecting high-speed materials the degree of shock heating during impact spallation. with the low degree of heating. [Kurosawa+18] Basalt -> Basalt (ANEOS) Thevimp =impact3.5 km/s-survival(The normalratecomponentduring theof launch5 km/s atis45likelydegrees)to be << 1. 1000 cells per projectile radius Elasto-plastic Survival rate afterHydrodynamicthe launch 0.1 is expected[Parametersto be highly are takenconservative from Ivanov+10]. With black circles Particles moving at >3.8 km/s Incipient melting

Sterilization

Acknowledgements: We thank the developers of iSALE, including G. Collins, K. Wünnemann, B. Ivanov, J. Melosh, and D. Elbeshausen. Aerodynamic heating Aerodynamic heating

Atmospheric condition

Composition: 95% CO2, 5% N2

T & r profile: Mars-GRAM 2005 v1.3 [Duvall+05; Justus+05]

Mars rocks Perfect sphere

Density: 2.8 x 103 kg/m3

Specific heat: 103 J/K/kg

Thermal conductivity: 2.3 W/m/K

The standard atmospheric model for Mars Emissivity: 0.95 [Duvall+05; Justus+05] A compressible flow solver JAXA Optimized Nonequilibrium Aerodynamic Analysis code (JONATHAN) [Fujita+06] Gas flow around 10 cm sphere Heat transfer rate

3.8 km/s at the ground condition

Trajectory analyses code[Fujita+12] -> The minimum size required for the penetration into the atmosphere is ~10 cm. Minimum size of Mars ejecta

<10 cm particles are largely affected by aerodynamic effects during the atmospheric passage.

We set the minimum size of Mars ejecta to be 10 cm. Thermal conduction

Maximum temperature distribution Flight path Survival angle (deg) rate (N/N ) 10 cm sphere 0 45 0.87

60 0.89

75 0.90

90 0.90 Sterilization condition: 773 K, >0.5 s The effects of aerodynamic heating on the microbe sterilization is minor. Orbital evolution Orbital calculation

Impact conditions: 45 degree SPH output were chosen to match Df of 10 km. (previous slide)

vimp: Rayleigh (6–18 km/s, 3 km/s step)

qimp: sin(2qimp) (15–90 deg., 15 deg. step)

Impact location: The Zunil location By assuming ballistic flight (7.7N, 166E) under Mars gravity Impact direction: NorthEast – East ※ Mars rocks are injected into the retrograde orbits, leading to frequent high-speed collisions.

Phase angle of the moons: Random Trajectory analyses Total 10,000 Monte Carlo runs Transport probability

To Phobos To Deimos

Elliptic Hyperbolic

Total transported mass from Mars to Martian moons 2.0 × 106 kg (Phobos) Mtransported= ൝ 3.8 × 104 kg (Deimos) Transported mass distribution Deimos average Phobos average

The averaged values were employed.

2.0 × 106 kg (Phobos) Mtransported= ൝ 3.8 × 104 kg (Deimos)

80% of Monte Carlo runs (8000 runs) result in the smaller mass transportation.

A 10-times mass transportation could occur. But, it is statistically rare. Difference from Chappaz+13 vej-Mej distribution

Velocity interval = 0.05 km/s

The Mars rocks launched at 4–5 km/s are efficiently transported to Phobos.

Oblique impacts produce Mars ejecta with the mass several times than vertical impacts. Total transported microbes Ntotal

8 Initial microbe density on Mars nMars = 10 CFU/kg

Survival rate after the launch = 0.1

Survival rate due to aerodynamic heating = 1

6 2.0 × 10 kg (Phobos) Total transported mass Mtransported = ൝ 3.8 × 104 kg (Deimos)

2.0 × 1013 CFU (Phobos) Total transported microbes Ntotal = ൝ 3.8 × 1011 CFU (Deimos) Outline 1. General assumptions

2. Transportation to the moons

3. Mars-rock bombardment on the moon

4. Background impact flux by natural meteoroids

5. The change in the Microbe density with time

6. Microbe contamination risk assessment

7. Conclusions Processes considered in this work Time sequence

Radiation sterilization

Impact sterilization Dispersion & fragmentation & Dust torus Continuous impacts of Crater formation background meteoroids formation

Radiation sterilization 20% of contaminated fragments mix with the regolith and retained in the collapsed lens. I. Craters III. Common area II. Covered area ~80% of contaminated fragments (slow) (quick) (moderate) are distributed globally, forming a thin layer (thickness ~0.1 mm) Characterization of Mars rocks -Size

-vimp & qimp distributions Size & Total number The size-frequency distribution of high-speed ejecta is highly uncertain. [Melosh11; Chappaz+13; Melosh+17]

For conservative estimate, “10 cm-assumption” was employed. -> All Mars rocks were assumed to be spheres with a diameter of 10 cm. ※The minimum size required for the penetration of the Martian atmosphere is ~10 cm. [Artemieva & Ivanov04; Our aerodynamic analysis]

6 The total number of Mars rocks = ൝1.4 × 10 (Phobos) 2.7 × 104 (Deimos)

The assumption yields the maximum contaminated area. vimp & qimp distributions Obtained in the orbital calculations

We extracted vimp & qimp for each Mars rock from the distributions by a Monte Carlo method. [e.g., de Niem+12; Kurosawa15; Kurokawa+18] The fate of projectiles 1. Fragmentation 2. Projectile retention or dispersion Fragmentation Longitudinal stress pulse in a penetrating Mars rock 2 into the regolith Pram ~ ρtvimp /2 ~ 4 GPa (at vimp = 2 km/s) 3 3 ρt = 2 x 10 kg/m cf., Compressive strength of intact basaltic rocks Y = 0.17-0.48 GPa [e.g., Mizutani+90] Impact fragmentation experiments of Basalt The largest fragment [Takagi+84] has ~1% of Mp. (~1 cm fragment)

Numbers = 100 x Pram/Y Projectile retention or dispersion

A much higher vtranslational compared to SterLim impact modeling vesc of the moons (~10 m/s). But, vtranslational would be lower than vesc from the Mars system (~3 km/s) -> Dust torus formation around Mars

Retained Mars-rock fragments stick around the wall of a growing crater.

[Patel+17, The meeting in the last year] Projectile retained fraction The dynamics of projectile deformation has not been fully understand. We employed the experimental data by Daly & Schultz (2016)

Data A basalt sphere impacting onto Daly & Schultz16 an asteroidal regolith analog at 4.5–5 km/s

Projectile retained fraction y

22% (Phobos) By convolving with the q distribution y = ቊ imp ave 29% (Deimos) Crater formation Mars-rock craters Regolith thickness of Martian moons ~ 20 m [Thomas98] much thicker than the Mars-rock diameter (10 cm) -> All the Mars-rock impacts occur on a granular layer. Projectile: Polycarbonate (4.8 mmf) Target: Dry sand (0.5 mmf) vimp = 6.8 km/s qimp = 90 degrees Frame rate = 300 fps Mars rock mixing with the regolith 1. The slope of a transient wall is steeper than the angle of repose of granular materials in general.

2. The wall of the transient crater collapses due to the gravity.

3. A granular flow directed to Granular flow the crater center is produced.

4. The retained Mars-rock fragments efficiently mix with the regolith.

5. A “collapsed lens” is deposited “Collapsed lens” [Melosh89] on the floor of a Mars-rock crater.

A thick regolith layer works as “a radiation shield” of the microbes. Mars rock mixing ratio in a collapsed lens

Final crater diameter Df

Transient crater depth Final crater depth Htr = Hf + Hb Hf = 0.2Df

π 3 Thickness of collapsed lens Mc= ρtDf 80 Hc = Hf/2

[Modified after The p-group scaling law Melosh89, Fig8.3] β 1 1 2β π 3 4π 3 ρp 3 1−β β Dtr = CD D g Vimp sin θimp [Schmidt & Housen87] 6 3 ρt p C = 1.4, β = 0.17, ρ = 2.7 x 103 kg/m3 An empirical relation between Dtr & Df D p and g = 0.0057 m/s2 for Phobos, Df = 1.25Dtr [Melosh & Vickery89] 0.003 m/s2 for Deimos Typical values from Monte Carlo runs

Typical final crater diameter ~10 m (~100 Dp)

Typical thickness of collapsed lenses ~1 m (~10 Dp)

Typical mixing ratio of a Mars rock in a collapsed lens ~10-5 (~10 ppm)

3.4% (Phobos) Access probability to the Mars-rock craters P =ቊ crater 0.28% (= Total coverage of the final craters on the moon’s surface) (Deimos)

σ 2 Pcrater = πDf /Smoon Gravity vs Strength

Two cratering regime Gravity: Y << ρgD Strengh- dominated Strength: Y >> ρgD

Calculated size on Phobos

Gravity- dominated

If the strength of the regolith on the moons less than 30–100 Pa, the cratering process is controlled by the gravity. Strength-dominated craters

An impact experiment using Gypsum block target [Suzuki+18]

Nylon (3.2 mmf) -> Gypsum

vimp = 3.4 km/s qimp = 90 deg Target tensile strength = 2.3 MPa Projectile size Gypsum target

Pre-impact surface

Cavity profile of a gravity-controlled final crater with the same cavity volume Strength-dominated craters Target strength prevent the crater collapse or reduce the degree of the collapse, resulting in the steep crater wall. The thickness of a collapsed lens under the strength-dominated regime is likely to be much thinner than the case of the gravity-dominated one. The “gravity-dominated cratering” assumption gives an upper limit pertaining to the survived number of the microbes.

Pre-impact surface

Cavity profile of a gravity-controlled final crater with the same cavity volume Scattered fragments Dust torus Dispersed Mars-rock fragments and escaped regolith particles produce a dust torus around Mars. [Modified after Ramsley & Head13] (a) 29 min (b) 76 min (c) 105 min

Launched radially at 800 m/s (d) 175 min (e) 280 min (f) 460 min

Nearly all ejecta fragments that remain in orbit of Mars return to Phobos within ~ 103 years [Hamilton and Krivov, 1996] The mass of dust torus The mass of dispersed projectile Mdis,p = (1-휓)Mp ~1 kg

The escaped mass of the regolith particles 3 vesc −3μ Mdis,t = CVρtRtr ~102 kg gRtr π 3 Given by the point-source theory cf., Total excavated mass Mexc = 6 ρtRtr [Holsapple & Housen82; Housen+83] [e.g., Croft80] ~2 x 104 kg

Cv = 0.32, Rtr = 0.5Dtr, and m = 0.4 The mixing ratio of the Mars-rock fragments in a dust torus ~1%

1 × 108kg (Phobos) The mass of dust torus Mtorus = ൝ 3 × 106 kg (Deimos) A global thin layer The dust particles are expected to be re-accumulated into the uppermost surface of the moons within several orbital periods. (~100 hours)

M 30 mm (Phobos) The thickness of the global layer L = torus = ቊ global ρtSmoon 1 mm (Deimos) Infinitesimal dust particles are assumed.

The small particles (1–10 mm) are removed from the Mars system due to radiation pressure within several hours. [Ramsley & Head13]

We assumed Lglobal = 0.1 mm.

This assumption does not change the conclusion of this study unless the thickness is thicker than 0.3 mm because the time constant TC for radiation-induced sterilization is nearly constant (71 years) for the layer with a thickness of < 0.3 mm. Rapid sterilization of the microbes in the thin layer

More than 70% of Mars rocks are concentrated into the global thin layer.

Required time for radiation-induced sterilization

0.1휉푎푣푒푁푀푎푟푠 1.2 × 103 years(Phobos) treq = 71ln = ൝ 푁푡ℎ 1.4 × 103 years(Deimos)

The major fraction of the transported microbes must be extinct until now. Outline 1. General assumptions

2. Transportation to the moons

3. Mars-rock bombardment on the moon

4. Background impact flux by natural meteoroids

5. The change in the microbe density with time

6. Microbe contamination risk assessment

7. Conclusions Background impact flux of natural meteoroids Impact flux of natural meteoroids

Crater diameter on Mars (m) 4 22 180 1000 2.6 m (Phobos) ? D = ቊ pmax 1.6 m (Deimos)

? From crater SFD to Impactor SFD The p-group scaling law β 1 1 2β π 3 4π 3 ρp 3 1−β β Dtr = CD D g Vimp sin θimp 6 3 ρt p [Schmidt & Housen87]

Empirical laws between Df and Dtr −0.13 1.13 Df = max(1.25Dtr, 1.2 Dc Dtr ) Dc = 7 km for Mars [Pike88] For simple crater For complex crater Dc is the transition diameter from simple to complex craters

Vimp = 14 km/s We employed averaged values on Mars. [Ito & Malhotra06]

qimp = 45 degrees [Shoemaker62] Impact flux of natural meteoroids

Crater diameter on Mars (m) 4 22 180 1000 2.6 m (Phobos) ? D = ቊ pmax 1.6 m (Deimos)

? 2.5 −2.5 N >Dp =DpmaxDp vimp & qimp distributions of natural meteoroids Impact velocity distribution: Rayleigh [Zahnle+03]

Averaged impact velocity = vimp,ave 2 2 2 = vimp,ave,Mars − vesc,Mars + vesc,moons 13.4 km/s (Phobos) [Schmedemann+14] =ቊ 13.2 km/s (Deimos)

Impact angle distribution: sin(2qimp) [Shoemaker62] Ejecta thickness

The mass of ejecta at a velocity interval (vej, vej+dvej) [Housen+83] 3μ 3 2 −3μ−1 mej vej dvej = 3μCVρtRtr gRtr vej dvej

The ballistic range of the ejecta at the velocity interval Rb [Melosh89] v2 ej sinθ cosθ −1 gRmoon ej ej R = 2 Rmoontan b v2 1− ej cos2θ gRmoon ej

The surface area of the ejecta landing site for the velocity bin Sej Rb l is the arc angle between the impact point and S = 2πRmoonsinλdλ, where λ = ej Rmoon the ballistic range measured from the center of the moon.

Thickness of the ejecta deposit launched at the velocity interval Lej

mejdvej Lej = Sejρt Ejecta thickness vs distance v = 13.4 km/s On Phobos imp D = 1 m p qimp = 45 deg

Dp = 10 cm

Dp = 1 cm

Dp = 1 mm Lej = 3 mm treq ~ 0.1 Myr

Lej decrease with distance by follow the power law with an exponent -2.6

Consistent with the previous studies [e.g., Melosh89]

The minimum size of impactor Dpmin~1 mm Total number of impacts prior to complete sterilization

2×103 years 2.5 2.5 6.7 × 106 (Phobos) Ntotal,BG ~ DpmaxDpmin = ൝ 0.1 Myr 2.0 × 106 (Deimos)

The ratio of treq to the time after the Zunil-forming event. ※The impact rate on the Mars system in the past 3 Gyr is roughly constant. [e.g., Neukum et al., 2001; Schmedemann et al. 2014]

3 For conservative estimate, we used treq = 2 x 10 years. 7 This treq was obtained by assuming N0 = 10 CFU/kg. Cumulative surface area of the thick ejecta-deposit layer

Ntotal,BG, vimp & qimp distributions -> The same Monte Carlo model for Mars-rock bombardment

2 2 The surface area of the thick ejecta-deposit layer Sshield = π Rb,3mm− Rf

Rb,3mm is the distance from the impact point covered by the thick ejecta-deposit layer along with the surface

The possible covered fraction by the ejecta deposit

σ 푆푠ℎ𝑖푒푙푑 0.11% (Phobos) Player = = ቊ 푆푚표표푛 0.097% (Deimos)

99.9 % of the microbes in the global thin layer should be sterilized within ~2 x 103 years after the Zunil-forming impact event. Outline 1. General assumptions

2. Transportation to the moons

3. Mars-rock bombardment on the moon

4. Background impact flux by natural meteoroids

5. The change in the microbe density with time

6. Microbe contamination risk assessment

7. Conclusions Impact sterilization of Mars rocks × −6 1.8 Survival rate ξ ≡ NΤN0 = exp −9.5 10 Vimp

2.9 × 10−5 (Phobos) By convolving with the vimp distribution, 휉ave= ൝ 5.6 × 10−4 (Deimos)

vimp – Mass distribution Mass(Left Y) Velocity interval = 0.1 km/s

The most part of the Mars rocks

have vimp > 3 km/s. Cumulative [Hyodo+, to be submitted; Our trajectory analyses] First collisions with the moons leads to significant sterilization. Microbe density in a collapsed lens

REQ-10 criterion for 100-g sampling

Mp ncrater0=0.1ξnMarsψ (Mc+Mp) Microbe density (CFU/kg)

3.1 × 10−3 CFU/kg (Phobos) ncrater0,ave= ൝ 4.8 × 10−2 CFU/kg (Deimos) Radiation-induced sterilization in Mars-rock craters Radiation survival rate integrated over a given depth H at time t 휂(푡, 퐻) = Inside a collapsed lens 퐻 푡 ׬ exp − 푑ℎ 0 푇퐶(ℎ) 퐻 At t = 0.1 Myr Depth (cm) Survival rate 0.3 3.1 x 10-27 1 1.2 x 10-4 3 6.6 x10-2 6 0.11 10 0.14 휂(푡, 퐻) 30 0.2 60 0.24 100 0.31 Microbe column density beneath the ejecta blanket

The microbial column density immediately after the formation of the global thin layer

0.1ξavenMars 1−ψave Mtransported σthin0= Smoon

The change in the column density during 2 x 103 years t σthin(t) = σthin0exp − 71 years where t = iDt is the time at the i-th impact 3 and Dt = 2 x 10 years/Ntotal,BG.

The number of microbes protected by the ejecta-deposit layer Nlayer at the i-th impact

Nlayer = σthin(t)Sshield

−6 2 (Phobos) Averaged-microbial-column density SNlayer 1.0 × 10 CFU/cm sthin,ave = = ൝ of the covered-microbial thin layer SSshield 1.1 × 10−6 CFU/cm2 (Deimos)

※ For conservative estimate, further sterilization during 0.1 Myr is not considered. The change in survived microbe numbers on Phobos

Mars-rock bombardment on Phobos Now

Global dispersion Patchy distribution (Mars-rock craters) Impact sterilization

Global thin layer Total Craters Craters Radiation sterilization

Total number of transported microbes = 2 x 1013 CFU Total number of survived microbes up to the present = 4 x 107 CFU (2 ppm) Outline 1. General assumptions

2. Transportation to the moons

3. Mars-rock bombardment on the moon

4. Background impact flux by natural meteoroids

5. The change in the microbe density with time

6. Microbe contamination risk assessment

7. Conclusions Microbe distribution SterLim view Our view

Mars rock bombardment Homogeneous deposition by averaging -Patchy in the horizontal direction incoming flux to the uppermost layer -Depth-dependent 7 Total survived microbes =൝4.0 × 10 CFU c.f., 1.9 × 107 CFU Microbe column density 3.4% -8 -3 2 Access probability P =ቊ 10 –10 CFU/cm crater 0.28% Microbe distribution SterLim view Our view

Mars rock bombardment Homogeneous deposition by averaging -Patchy in the horizontal direction incoming flux to the uppermost layer -Depth-dependent 7 Total survived microbes =൝4.0 × 10 CFU c.f., 1.9 × 107 CFU Microbe column density -8 -3 2 Equivalent microbe 2.6 ×10−6 CFU/cm2 10 –10 CFU/cm =൝ column density 4.0 ×10−6 CFU/cm2 Microbe distribution SterLim view Our view

The sampling probabilities of the microbes from the Mars-rock craters

Ps,crater = Pcraterncrater(t,H)Ms ※ncrater(t,H) = η(t, H)ncrater0

The sampling probabilities of the microbes from the covered-microbial thin layer

Ps,layer = Playerσthin,aveSs

Note: Ms = rtSSHs Sampling mass The unit of ncrater(t,H) is CFU/kg. Ss Sampling area 2 The unit of σthin,ave is CFU/cm Hs Sampling depth Sampling probabilities r = 2 x 103 kg/m3 Global average: Ps = Ps,crater + Ps,layer t was assumed. Crater-avoiding: Ps = Ps,layer 10-5 100

(a)Phobos (b)Deimos

) 2 10-6 REQ-10 30

10-7 10 10-8

10-9

Sampling area (cm area Sampling Sampling probability Sampling 8 n0 = 10 CFU/kg 10-10 1 0.1 1 10 100 1 10 100 Sampling depth (cm) 5 cm (Phobos) Allowable sampling depth for the Unrestricted Earth return = ቊ 3 cm (Deimos) (100 g-sampling) There is no limit for 30 g-sampling. Sensitivity analysis

10 If we used nMars = 10 CFU/kg, the curves of Ps 2-orders shift to the upward.

10-3 100

(a)Phobos (b)Deimos

) 2 10-4 30

10-5 10 10-6 REQ-10

10-7

Sampling area (cm area Sampling Sampling probability Sampling 10 n0 = 10 CFU/kg 10-8 1 0.1 1 10 100 1 10 100 Sampling depth (cm)

We could also collect the regolith sample up to ~10 cm2 by crater-avoiding operations. Contamination risk from unrecognized craters

By introducing

Crater SFD on Mars “event probability” Pevent, [Hartmann05] we can address the risk by unfound craters.

Formation age Pevent (years) 106 1 105 0.1 104 0.01 103 0.001 102 0.0001

vimp & qimp distributions from the unfound crater were obtained by assuming fully-randomized impact locations and directions. The change in survived microbe numbers on Phobos

Mars-rock bombardment on Phobos Now

Global dispersion Patchy distribution (Mars-rock craters) Impact sterilization

Global thin layer Total Craters Craters Radiation sterilization

Ps = Pevent(Ps,crater + Ps,layer) Ps = PeventPs,crater + Ps,layer Contamination risk from unrecognized craters (100 years)

Ps = Pevent(Ps,crater + Ps,layer) ~ PeventPs,layer = PeventxaveNtotalSS

-5 xave : Impact survival rate = 2.9 x 10 13 Ntotal : Transported microbes = 2 x 10 CFU

Zunil-sized unfound craters with the formation age of 100 years are highly unlikely. -> The contamination risk by the young unfound crater can be negligible. Contamination risk from unrecognized craters (>10 kyr)

10-5 100

(a) 60 g sampling (b)100 g sampling

) 2 30

REQ-10 10-6 10 10 kyr

10 kyr 3

3 kyr

Sampling area (cm area Sampling Sampling probability Sampling 3 kyr 10-7 1 0.1 1 10 100 1 10 100 Sampling depth (cm) Ps = PeventPs,crater + Ps,layer ~ PeventPs,crater h(t,H) and Pevent(t) are competitive. -> Complex behavior in Ps against the changing depth. We could rule out the contamination risk from unfound craters down to ~10 cm from the surface of Phobos if the sampling mass could be limited to <60 g. Known craters on Earth

Mojave size Tooting size

Zunil size Crater diameter (km) diameter Crater

1 Myr Known craters on Earth

Mojave size Tooting size Zunil size

Crater diameter (km) diameter Crater The craters found on Earth have been precisely dated. Although the crater1 Myr chronology model for Mars has a large uncertainty, unfound 10 km-sized crater having <1 Myr age is highly unlikely. Propagation of uncertainties

Ps = Ps,crater + Ps,layer ~ Ps,crater

Ps,crater = Pcraterncrater(t,H)Ms ∝ Mtransported휂(푡, 퐻)abξ푎푣푒ψavenMarsrtSSHs

Current analyses a: Survival rate during the launch 0.1 8 nMars : Potential microbe density on Mars 10 CFU/kg b: Mixing ratio of Mars rocks to collapsed lens ~10 ppm x : Impact survival rate 2.9 x 10-5 y: Projectile retained fraction 0.22 h: Radiation survival rate

퐻 푡 ׬ exp − 푑ℎ 휂(푡, 퐻) = 0 푇퐶(ℎ) 퐻 Averaged transported mass Maximum transported mass

Fitting line Pcrater = 1.68 x 10-8 x M Propagation of uncertainties

Ps = Ps,crater + Ps,layer ~ Ps,crater

Ps,crater = Pcraterncrater(t,H)Ms ∝ Mtransported휂(푡, 퐻)abξ푎푣푒ψavenMarsrtSSHs

퐻 푡 ׬ exp − 푑ℎ 휂(푡, 퐻) = 0 푇퐶(ℎ) 퐻 Conclusions

☆ We re-visited the launch of Mars rocks and their orbital evolution by using advanced numerical methods.

☆ We constructed the spatial distribution of the Mars rocks based on our best knowledge about impact physics.

☆ The microbe density is patchy in the horizontal direction and depth-dependent.

☆ The survived fraction of the transported microbes is only ~2 ppm for Phobos and ~50 ppm for Deimos.

☆ Microbial contamination probability of collected samples can be easily made below 10-6 by choosing appropriate sampling approaches. Sample return missions from the Martian moons can be classified as Unrestricted Earth return. Q6 TR 2018-00-17C

Comparative Risk Assessment between Samples from Martian moons & Natural Influx

September 19, 2018 Rev.C September 14, 2018

Kazuhisa Fujita Institute of Space & Astronautical Science, Japan Aerospace Exploration Agency Kosuke Kurosawa Planetary Exploration Research Center, Chiba Institute of Technology Hidenori Genda, Ryuki Hyodo Earth-Life Science Institute, Tokyo Institute of Technology Takashi Mikouchi The University Museum, The University of Tokyo Phobos/Deimos Microbial Contamination Assessment Team Japan Aerospace Exploration Agency TR 2018-00-17C A Comparative Risk Assessment of Samples from Martian Moons & Natural Influx

Document Revision History 106

Revision Status and Description Date Author First release 14/09/2018 Fujita, K. et al. A Data of Martian meteorites are updated. Detailed 16/09/2018 Fujita, K. descriptions about aerodynamic heating in the terrestrial atmosphere are added. B Descriptions about the Martian meteorite with a 0.2-m 18/09/2018 Fujita, K. and diameter are added. Kurosawa, K. C Comparison to direct sample return from Mars is added. 19/09/2018 Fujita, K. TR 2018-00-17C A Comparative Risk Assessment of Samples from Martian Moons & Natural Influx

Summary 107  According to COSPAR planetary protection policy (PPP), determination as to whether a sample return mission is classified “Restricted Earth return” or not shall address the six questions, the sixth of which goes Does the preponderance of scientific evidence indicate that there has been a natural influx to Earth, e.g., via meteorites, of material equivalent to a sample returned from the target body?  Based on the estimation of microbial contamination probability of Martian meteorites obtained by Fujita et al. (2018), and on the preceding study of Mileikowsky et al. (2000a, 2000b) and Horneck et al. (2002), it is clearly proven that the answer to the sixth question is Yes.  Martian meteorites transported from Mars in the past 1 Myr have microbial contamination probability much higher by order of magnitude (103 or more) than that of 100-g samples taken from Martian moons. This means that natural influx equivalent to samples from Martian moons is continuously transported to the surface of Earth.  For this reason, it is considered that sample return from the Martian moons is classified as Unrestricted Earth Return, provided that total mass of samples is limited within 100 kg. TR 2018-00-17C A Comparative Risk Assessment of Samples from Martian Moons & Natural Influx

Physical Processes 108

Reformation of Martian moons surface by natural meteoroid Sterilization by radiation impacts

Sterilization during hypervelocity impact on surface of Martian Distribution of Mars ejecta fragments moons by impact, recirculation, and re-impact

Mars ejecta formation and transportation from Martian Sterilization by radiation surface

Sterilization during Mars ejecta formation (hypervelocity impact) Sterilization by aerodynamic heating Potential microbial density on Martian surface No impact sterilization TR 2018-00-17C A Comparative Risk Assessment of Samples from Martian Moons & Natural Influx

Identified Martian Meteorites in the Past 1 Myr 109  List of latest Martian meteorites having cosmic-ray exposure ages less than 1 Myr  Cosmic-ray exposure ages are taken from Aoudjehane et al. (2012), Nishiizumi et al. (2011), Park et al. (2003), Schwenzer et al. (2007), and Wieler et al. (2016). Ejection age is expected to be a sum of cosmic-ray exposure age and terrestrial age.  Total mass of Martian meteorites collected on the terrestrial surface amount to 40 kg, which is expected to be only the tip of the iceberg.

Martian meteorite Mass (kg) Cosmic-ray exposure ages (Myr) Ejection age (Myr) EETA 79001 7.94 ~ 0.6 ~ 0.6 NWA 4925 0.282 ~ 0.7 ~ 1.1 Sayh al Uhaymir 005-150 11.21 ~ 1.0 ~ 1.0 NWA 1195 0.315 ~ 1.0 ~ 1.2 NWA 5789 0.049 ~ 1.0 ~ 1.0 NWA 6162 0.089 ~ 1.0 ~ 1.0 Tissint 7-11 ~ 1.0 ~ 1.0 NWA 2046 0.063 ~ 1.0 ~ 1.2 NWA 2626 0.0311 ~ 1.0 ~ 1.3 Dar al Gani 476-1051 10.45 ~ 1.0 ~ 1.0 TR 2018-00-17C A Comparative Risk Assessment of Samples from Martian Moons & Natural Influx

Comparison between Sample Return & Natural Influx 110

 If microbial survival rate (MSR) against radiation is higher than expected, contamination probabilities are higher in both cases by the same order of magnitude.  Even if MSR against hypervelocity impact may is higher than expected, it may be improbable to exceed a 103 times prediction, according to past impact experiments in the literature.  MSR of Martian meteorites quickly increases with diameter.

Impact sterilization Distribution Radiation Sampling on Phobos surface & dilution sterilization by 100 g Impact sterilization in (x ~ 10-4) (x ~ 10-4) (x ~ 10-4) (x < 0.1) Mars ejecta formation Mars ejecta Diluted Sterilized (x 0.1) fragments fragments fragments ~ 103 ~ 10-1 ~ 10-5 Mars < 10-6 On Mars ejecta (CFU/kg) (CFU/kg) (CFU/kg) 8 7 10 10 Mars ejecta Decelerated Meteorites (CFU/kg) (CFU/kg) as meteorites meteorites on ground > 10-3 > 10-4 > 10-4 » 10-3 Sampling (CFU/kg) (CFU/kg) (CFU/kg)

by 100 g

direct Earth Radiation sterilization Aeroheating NO impact Retrieved ~ 107 on orbit (1 Myr) sterilization sterilization meteorites (x > 10-10) (x > 10-1) (x 1) (» 40 kg) TR 2018-00-17C A Comparative Risk Assessment of Samples from Martian Moons & Natural Influx

Radiation Sterilization of Martian Meteorite 112  Essential Characteristics  According to radiation sterilization model (see Sec. 7 of Fujita et al., 2018), total microbes surviving after 1 Myr amount to 4.1x10-3 CFU (MSR = 4.1x10-10) for a meteorite having a 0.1-m diameter (1 kg in weight) , which is a threshold diameter for escape from Mars.  Martian meteorites having larger diameters, which are more likely to arrive at Earth, have much higher MSR because of slower radiation sterilization in the deep region (3.6x10-8 for D = 0.2 m) . Above all, MSR > 10-10 for all Martian meteorites generated in the past 1 Myr.

D = 0.1 m D = 0.2 m TR 2018-00-17C A Comparative Risk Assessment of Samples from Martian Moons & Natural Influx

Aerodynamic Deceleration &Heating on Earth Entry 113  Characteristics of Terrestrial Aerodynamic Heating  Because of a dens atmosphere, Martian meteorites arriving at Earth undergo much higher aerodynamic heating than they did during the Mars escape phase in the Marian atmosphere (see Sec. 5 of Fujita et al., 2018).  Martian meteorites are completely decelerated by aerodynamic drag to terminal velocities (< 100 m/s for D < 0.4 m), resulting in no impact sterilization on the ground. TR 2018-00-17C A Comparative Risk Assessment of Samples from Martian Moons & Natural Influx

Aerodynamic Heating Sterilization on Earth Entry 114  Characteristics of Terrestrial Aerodynamic Heating  Heat conduction analysis of Martian meteorites along the atmospheric entry trajectory (with an assumption of Vinf = 5 km/s) shows that MSR > 0.1 for meteorites larger than 0.1 m in diameter (based on 500ºC x 0.5 sec sterilization), even though uncertainties originating from ablation, erosion, and fragmentation are taken into account. TR 2018-00-17C A Comparative Risk Assessment of Samples from Martian Moons & Natural Influx

Conclusions 115  Martian meteorites transported from Mars to Earth in the past 1 Myr have microbial contamination probability much higher by order of magnitude (103 or more) than that of 100-g samples taken from Martian moons.  Errors in radiation sterilization model do not change this conclusion because microbial contamination probabilities of samples and meteorites changes accordingly at the same order of magnitude.  Errors in hypervelocity impact sterilization model do not change this conclusion, since the microbial survival rate against hypervelocity impacts is expected to remain below 0.1.  Aerodynamic heating has minor contributions to sterilization of Martian meteorites on arrival at Earth.  The above means that natural influx equivalent to samples from Martian moons is continuously and frequently transported to the surface of Earth.

 According to COSPAR planetary protection policy (PPP), since the preponderance of scientific evidence indicates that there has been a natural influx to Earth of material equivalent to a sample returned from the target body, sample return from the Martian moons is classified as Unrestricted Earth Return. TR 2018-00-17C A Comparative Risk Assessment of Samples from Martian Moons & Natural Influx

References (1/2) 116 1. Fujita, K., Kurosawa, K., Genda, H., Hyodo, R., Mikouchi, T., and Matsuyama, S., 2018. Assessment of Microbial Contamination Probability for Sample Return from Martian Moons. JAXA Technical Document GNG-2018003. 2. Mileikowsky, C., Cucinotta, F. A., Wilson, J. W., Gladman, B., Horneck, G., Lindegren, L., Melosh, J., Rickman, H., Valtonen, M., and Zheng, J. Q., 2000a. Natural Transfer of Viable Microbes in Space: 1. From Mars to Earth and Earth to Mars. Icarus, 145, 391–427. 3. Mileikowsky, C., Cucinotta, F. A., Wilson, J. W., Gladman, B., Horneck, G., Lindegren, L., Melosh, J., Rickman, H., Valtonen, M., and Zheng, J. Q., 2000b. Risks threatening viable transfer of microbes between bodies in our solar system. Planetary and Space Science, 48, 1107-1115. 4. Horneck, G., Mileikowsky, C., Melosh, H. J., Wilson, W. J., Cucinotta, F. A., and Gladman, B., 2002. Viable Transfer of Microorganisms in the Solar System and Beyond. in Astrobiology, edited by Horneck, G. and Baumstark-Khan, C. Springer-Verlag Berlin Heidelberg, Springer, Berlin, Heidelberg, Chapter 4, 57-76. 5. Aoudjehane H. C., Avic G., Barrat J.-A., Boudouma O., Chen G., Duke M. J. J., Franchi I. A., Gattacceca J., Grady M. M., Greenwood R. C., Herd C. D. K., Hewins R., Jambon A., Marty B., Rochette P., Smith C. L., Sautter V., Verchovsky A., Weber P., and Zanda B., 2012. Tissint Martian meteorite: A fresh look at the interior, surface, and atmosphere of Mars. Science, 338, 765-788. 6. Nishiizumi K., Nagao K., Caffee M. W., Jull A. J. T., and Irving A. J., 2011. Cosmic-ray exposure chronologies of depleted olivine-phyric shergottites. Lunar Planet. Sci. 42, Lunar Planetary Institute, Houston, #2371 (abstract). TR 2018-00-17C A Comparative Risk Assessment of Samples from Martian Moons & Natural Influx

References (2/2) 117 7. Park, J., Okazaki, R., and Nagao, K., 2003. Noble gas studies of Martian meteorites: Dar al Gani 476/489, Sayh al Uhaymir 005/060, Dhofar 019, Los Angeles 001 and Zagami. Lunar Planet. Sci. 34, Lunar Planetary Institute, Houston, #1213 (abstract). 8. Schwenzer, S. P., Herrmann, S., Mohapatra, R. K., and Ott, U., 2007. Noble gases in mineral separates from three shergottites: Shergotty, Zagami, and EETA79001. Meteoritics and Planet. Sci., 42, 387-412. 9. Wieler, R., Huber, L., Busemann, H., Seiler, S., Leya, I., Maden, C., Masarik, J., Meier, M. M. M., Nagao, K., Trappitsch, R., and Irving, A. J., 2016. Noble gases in 18 Martian meteorites and angrite Northwest Africa 7812- Exposure ages, trapped gases, and a re-evaluation of the evidence for solar cosmic ray-produced neon in shergottites and other achondrites. Meteoritics and Planet. Sci., 51, 407-428. 10. Burchell, M. J., Mann, J. R., and Bunch, A. W., 2004. Survival of bacteria and spores under extreme shock pressures. Mon. Not. R. Astron. Soc., 352, 1273–1278. 11. Horneck, G., Stöffler, D., Eschweiler, U., and Hornemann, U., 2001. Bacterial Spores Survive Simulated Meteorite Impact, Icarus, 149, 285–290. 12. Stöffler, D., Horneck, G., Ott, S., Hornemann, U., Cockell, C. S., Moeller, R., Meyer, C.,, de Vera, J.-P., Fritz, J., and Artemieva, N. A., 2007. Experimental evidence for the potential impact ejection of viable microorganisms from Mars and Mars-like planets. Icarus, 186, 585–588. 13. Price, M. C., Solscheid, C., Burchell, M. M., Josse, L., Adamek, N. Cole, M. J., 2013. Survival of yeast spores in hypervelocity impact events up to velocities of 7.4 km s-1. Icarus, 222, 263–272. Items Impact direction of the Zunil-forming impact

North East

Our Monte Carlo model

East

[Preblich+07, JGR] The ejecta having the retrograde orbits

Deimos Orbital speed 1.4 km/s

North pole of Mars

Phobos Orbital speed 2 km/s Pcrater vs Cumulative mass of Mars rocks Player vs Cumulative mass of meteoroids

Pcrater Player

Pcrater & Player are roughly proportional to Cumulative mass of impactors. Effects of impact direction on Mtransported & vimp

Ψ = 0 – 360 deg (Random) North Ψ = 225 deg

West East

Ψ = 225-270 deg (NorthEast- East)

South Ψ = 0 deg

The mass fraction at vimp < 2 km/s Mtransported Ψ : 0 – 360 deg -> 13% Ψ : 0 – 360 deg -> 1.46 x 106 kg Ψ : 225 – 270 deg -> 0.4% Ψ : 225 – 270 deg -> 2.04 x 106 kg Mojave crater chronology

[Werner+14] Transported mass to Phobos from five large craters on Mars

Average Mojave: 3.9914e+08 Tooting: 5.8380e+07 McMurdo: 7.2231e+06 Corinto: 4.4108e+06 Zunil: 1.4661e+06 Uncertainty in impact-survival rate

Sampling probability in the “Maximum case”

On Phobos

[Patel+18]

By convolving the vimp distribution -5 Nominal: N/N0 = 2.9 x 10 -4 Maximum: N/N0 = 3.2 x 10 (On Phobos) Radiation survival rate h(t, H)

휂(푡, 퐻) = 퐻 푡 ׬ exp − 푑ℎ 0 푇퐶(ℎ) 퐻 Transportation probability

Our study Chappaz+13

To Phobos

Elliptic Hyperbolic

To Phobos Table 1

Phobos Deimos Transported mass (kg) 2.0E+06 3.8E+04 Transported microbes (CFU) 2.0E+13 3.8E+11 Number of impacts of Mars rocks 1.4E+06 2.7E+04 Median impact velocity (km/s) 3.6E+00 3.2E+00 Impact survival rate 2.9E-05 5.6E-04 Projectile retained fraction 2.2E-01 2.9E-01 Mars rock mixing ratio in crater 1.0E-05 1.1E-05 ncrater0 (CFU/kg) 3.1E-03 4.8E-02 Pcrater 3.4E-02 2.8E-03 Radiation survival rate at 1 m depth 3.1E-01 3.1E-01 sthin0 (CFU/cm2) 2.9E-05 3.3E-05 sthin (CFU/cm2) 1.0E-06 1.1E-06 Player 1.1E-03 9.4E-04 Nsurv,crater (CFU) 4.0E+07 1.9E+07 Nsurv,layer (CFU) 1.7E+04 4.9E+03 Survived fraction at the present 2.0E-06 5.1E-05 Table 2

Depth from the surface (cm) Survival rate 0.3 3.1E-27 1 1.2E-04 3 6.6E-02 6 1.1E-01 10 1.4E-01 30 2.0E-01 60 2.4E-01 100 3.1E-01 Mojave

Tooting McMurdo

Corinto

Zunil

#Name Diameter(km) Ejecta_mass (kg) 1σ (kg) Mojave 58 5.28E+14 2.90E+14 Tooting 29 5.34E+13 2.09E+13 McMurdo 23 2.41E+13 1.36E+13 Corinto 13.5 3.27E+12 1.79E+12 13 Zunil 10.1 1.57E+12 1.10E+12 Mp ~ 1 x 10 kg 12 km/s, Basalt -> Basalt 衝突放出計算(玄田)

30 degree 45 degree

60 degree 75 degree

地表面より上空にあり, >3.5 km/sの速度で運動している粒子のデータを出力. 軌道計算(兵頭, 計算中) 計算の1例

SPH粒子の軌道をN体軌道計算, 解析計算で追跡し, 結果が一致することを確かめた.

計算コードが概ね完成. 現在計算中. 計算出力待ち, 結果の解析, 吟味, まとめなど随時進める予定... フォボスへの衝突時の加熱

強度モデルパラメータ Basalt->Basalt, 正面衝突, 250 CPPR [Ivanov+10, GSA special paper]

1 km/s 2 km/s 4 km/s

Projectileの裏面まで>600 Kまで加熱するには4 km/sの速度が必要か...?